Eight Nobel laureates including Archbishop Desmond Tutu have written to the prime minister to argue that oil derived from Canadian tar sands "threatens the health of the planet" and that the UK should support European moves to classify the controversial energy source as highly polluting.

A similar letter has been sent this week to the transport minister, Norman Baker, by the shadow transport secretary, Maria Eagle, asking him "to vote in favour of labelling oil from tar sands as highly polluting immediately and in line with the European commission's proposals".